Seal for rotary device

ABSTRACT

A rotary piston engine in which the spring-biased apex seals of the rotor are counterbalanced, whereby to limit the effect of centrifugal force on the pressure of the seals against the internal wall of the engine chamber.

United States Patent 1191 Clough, Jr.

[ 1 Sept. 9, 1975 SEAL FOR ROTARY DEVICE [76] Inventor: Roy L. Clough, Jr., l N. Curtisville Rd., Concord, NH. 0330] [22] Filed: Mar. 14, 1974 [2H Appl. No.1 451,098

I I/I'll 1547.45! [2/1970 Milot ct al. 4l8/l l5 FOREIGN PATENTS OR APPLICATIONS l,925,l25 ll/l970 Germany 4lH/l 15 Primary Examiner-C. J. Husar Assistant Examiner-L. J. Casaregola Attorney, Agent, or Firm-Schiller & Pandiscio [57] ABSTRACT A rotary piston engine in which the spring-biased apex seals of the rotor are counterbalanced, whereby to limit the effect of centrifugal force on the pressure of the seals against the internal wall of the engine chamber.

l Claim, 3 Drawing Figures PATENTED SEP 9 i975 SEAL FOR ROTARY DEVICE This application relates to rotary engines and more particularly to seals for such engines.

ln recent years, many attempts have been made to eliminate the reciprocating piston engines low efficiency crankshaft while retaining its advantage of high intermittent temperatures. Of the thirty or forty different types of engines which have been suggested to date for such a purpose, great attention has been given to rotary-piston engines.

Of all the rotary-piston engines known, the ones which are now being given a great deal of consideration are those generally described as ecccntric-rotor en gines, and more specifically, Wankel rotary combustion engines. The eccentric-rotor engine usually comprises a rotor, which is eccentrically mounted on a drive shaft so that it moves in one direction inside a specific geometrically designed chamber. In the case of the Wankel engine, the rotor is three-cornered and it rotates inside a trochoid-shaped chamber.

The rotor is shaped so that is divides the chamber into a plurality of smaller compartments. Each compartment is the analogue of the cylinder in the standard reciprocating-piston engine since as the rotor rotates, all four phases of the standard internal combustion cycle occur, i.e., intake, compression, power and ex hausl, Thus, rotor tip or apex seals (which serve the same function as piston rings in a conventional reciprocating piston engine) must be employed to provide a dynamic seal which will effectively operate under high temperature conditions, between the rotor apices and the inner surfaces of the chamber.

As described in the article Rotary Engines by Wallaeh Chinitz, published in Scientific American, February 1969, Volume 220 at page 96, one type of seal which has been devised for the Wankel type engine is provided with springs that maintain light pressure against the trochoidal surface of the internal chamber. These seals heretofore, however, have proven unsatisfactory. Generally, comparatively hard casing surface materials are used on the inside of the chamber, while relatively soft materials are used to make these seals. As the speed of the rotor increases, the pressure between the trochoidal surface and the seals increases. This increases the wear and decreases the service life of the seals as compared to the conventional piston rings. Auxiliary lubrication, by simply adding a lubricant to the fuel, may be provided to reduce seal wear. However, this tends to lead to starting problems in cold weather and production of undesirable emissions due to pyrolysis of the lubricant.

It is, therefore, a principal object of the present invention to provide in a rotary piston engine a novel tip seal for the rotor, which seal overcomes many of the deficiencies of the prior art.

Another object of the present invention is to provide a rotor tip seal which will provide an optimum minimum scaling pressure against the surface of the engine chamber at idle and low speeds and includes means for limiting or preventing increases in sealing pressure with increasing rotor speeds.

To effect the foregoing and other objects, the present invention comprises a rotor of a rotary piston engine having a tip seal which is spring biased against the chamber surface and which also is influenced by a counterweight so that as the rotor speed increases,

thereby increasing the centrifugal force applied to the seal, a countering centripetal force is also applied to the seal to prevent an increase in seal pressure.

Other objects of the present invention are disclosed or are rendered obvious hereinafter, The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims. For a fuller understanding of the nature and objects of the present invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

FIG. 1 is a schematic crossscctional view showing the housing and rotor assembly ofa Wankel-type rotary engine in which tip seals of the present invention are used;

FIG. 2 is an enlargement ofa portion of FIG. I showing in cross-section details ofa tip seal assembly constituting a preferred embodiment of the present invention; and

FIG. 3 is an exploded perspective view of the tip seal assembly shown in FIG. 2.

In the drawing, like numerals refer to like parts.

Referring now to FIG. I, a typical Wankel rotary engine comprises a housing 20 which includes peripheral intake and exhaust ports 22 and 24 respectively and a hollow chamber 26. The internal wall 28 of chamber 26 is formed as a trochoid in two dimensions and linear in a third. Mounted for rotation about a centrally disposed shaft 30 is rotor 32. The latter is connected to shaft 30 through planetary gears (not shown) which are used to transmit torque. Rotor 32 has three radially extending vanes or lobes, e.g., is substantially triangular in cross section, and is disposed so that as it is turned by shaft 30 through the connecting planetary gears, each of the apices of the vanes thereof moves in follower relation in substantially continuous contact with the epitrochoid curve of wall 28. The vanes thus divide the chamber 26 into a plurality of compartments, each of which is an analogue of the cylinder in the standard reciprocating piston engine. The events in one compartment are repeated sequentially in the other compartments as the rotor makes one complete revolution. Thus, as shown in FIG. 1, compartment A is in its intake phase, compartment B is in its compression phase, and compartment C is in its exhaust phase.

To prevent gas from leaking between the compartments, each of the apices of rotor 32 are fitted with spring-mounted seals which are represented schematically at 34.

Referring now to FIGS. 2 and 3, in accordance with this invention, the conventional seals 34 are replaced with apex seal assemblies which are identified generally as 34A. Each seal assembly 34A comprises an elongated seal element in the form of a planar slab 36, one edge 37 of which is flat and the other edge 38 of which is curved along one side so as to provide a wear line to be placed in sliding contact with the internal engine wall 28. One side of the seal element 36 is provided with a longitudinally extending groove 40 which is substantially parallel with the edges 37 and 38 and preferably but not necessarily extends along the entire length of the seal element. Each assembly 34A also comprises a counterbalancing element 42. The latter is also substantially planar and has a lip 44 adapted to loosely fit in groove 40 of the slab 36, a rib section 46 and a counterweight section 48 along the edge opposite lip 44 and parallel thereto. The length of the seal element 36 is at least equal to the depth (i.e., axial dimension) of the rotor and the length of element 42 preferably is the same as that of groove 40.

Each apex of rotor 32 is provided with a radially directed slot 50 along the entire depth of the rotor. A corresponding seal element 36 is slidingly disposed in slot 50 with its flat edge 37 directed toward the rotor shaft 30. The width of each slot 50 is such as to provide a snug sliding fit for the corresponding seal element The seal element is disposed so that the curved side of its edge 38 leads" the seal element in its movement along engine surface 28. Means are provided. typically in the form of compression springs 54 located in slot 50 between the bottom of the latter and the inner edge 37 of each seal element 36, for urging the latter radially outward beyond the apex of the rotor vane against the surface of the wall 28 with an optimum minimum sealing pressure.

Each apex of rotor 32 also is formed with a second slot 52 that extends at about a right angle to and communicates with slot 50. The length of slot 52 is at least as great as that of element 42. Each slot 52 is shaped in crosssection so as to provide opposed concave surfaces 56 that define a channel for receiving the rib section 46 of the counterbalancing element and a circularly curved surface 57 that forms a large clearance channel 58 to accommodate the counterweight section 48. Surfaces 56 are shaped and spaced so as to engage and function as a pivot support or bearing surface for rib section 46, while channel 58 is oversized with respect to counterweight section 48 so as to permit limited freedom of pivotal movement for the counterbalancing element. On each side of each concave surface 56 as seen in FIG. 2, the slot 52 has flat surfaces 59 and 60, and each surface 59 and 60 is spaced from its counterpart far enough to provide the clearance required for limited pivotal movement of the counterbalancing element,

Each counterbalancing element 42 is disposed in a slot 52 as shown with surfaces 56 slidably engaging its rib section 46, and with its lip 44 protruding into groove 40 of seal element 36. Preferably the end edge of lip 44 is rounded as shown so as to prevent binding and thereby facilitate pivotal movement of the lip relative to the seal element.

When each seal assembly is so mounted in an apex section of the rotor, the masses of the seal element 36 and the counterweight portion 48 provide opposing moments with respect to the pivot point provided by rib section 46 and bearing surfaces 56. The springs 54 are selected so as to press the seal element 36 against the inner surface 28 of the engine housing with an optimum minimum pressure when the rotor is stationary or rotating at idle or relatively low speeds.

In operation, as the rotor turns, centrifugal force will act on seal element 36 and also on counterweight section 48 of counterbalancing element 42. Because the latter is pivoted between its ends, the centrifugal force acting on counterweight section 48 will produce a countering force that tends to balance off the centrifu gal and spring forces acting on the seal element and thereby prevents or at least limits increases in seal pres sure. It is to be understood that by properly dimensioning the counterbalancing element, it is possible for it to apply a countering force to the seal element whereby to substantially effectively cancel the effect of the centrifugal force of the seal element per se, whereby the sealing pressure exerted by the seal element will be substantially independent of rotor speed and instead be determined substantially solely by the forces exerted by springs 54. However, since sealing is a dynamic as well as static function, it is preferred to calculate the counterweight mass and the countering moments so that at high speeds the counterbalancing element acts to reduce the rubbing pressure exerted by the seal element on the surrounding surface 28 due to springs 54, so as to reduce friction drag on the rotor as well as friction wear on the seal elements.

Obviously, certain changes can be made to the above-described apparatus without departing from the spirit of the invention. For example, compression springs 54 can be replaced by a single leaf spring. Additionally, the channel 58 may be shaped so as to confine pivotal movement of the counterbalancing element between two predetermined limit positions whereby to limit the extent to which the seal can be forced outwardly by springs 54 or forced inwardly by the countering force exerted by the counterbalancing element. Also, the lip section of the counterbalancing element could be pivotally connected to the seal element by a pivot pin. Another possible modification is to form the seal assembly as a one-piece unit having a U- or W shaped configuration, wherein one half of the unit would function as sea] element 36 and be biased by springs like springs 54, the other half would function as the counterbalancing element 42, and the center would be pivotally coupled to the rotor in the manner of rib section 46. The apexes of the rotor would be provided with U- or W-shaped slots to accommodate such seals as well as the spring'biasing means.

Another possible modification consists of omitting springs 54 and replacing them with one or more springs that act directly on the counterbalancing element 42 to bias the seal element against surface 28 with a suitable sealing pressure.

Although the slot 52, counter balancing element 42 and groove 40 of the seal element 36 are preferably all disposed on the trailing side of the seal in its movement along the engine surface, as shown, they can also be disposed on the leading side of the seal.

It is to be understood that seals constructed accord ing to the present invention may be employed in other forms of rotary engines and also may be used in fluid motors and pumps wherein a rotor or impellor makes sliding contact with a surrounding wall. With respect to fluid motors and pumps, the invention may be practiced as described above. As a further modification it may be desireable to dimension the counterbalancing element so that as the rotor speed increases, the element applies a countering force to the seal element which increases at a greater rate than the effect of the centrifugal force on the seal element per se, whereby the sealing pressure will be reduced to zero and the seal will leak at a predetermined speed of the rotor. This de' sign is particularly useful to avoid over pressure in air compressors, or no-load overspeeding in air driven tools, such as grinding wheels.

What is claimed is:

l. A rotary engine comprising:

a housing having an internal chamber defined by a curved surface;

a rotor unit mounted for rotation in said chamber and having a plurality of lobes which move with said rotor in follower relation with said curved surface; and

a sealing means associated with each lobe for providing a sealing contact with said curved surface, said sealing means comprising a first slot in a lobe of said motor extending radially inward from the apex of said lobe. a second slot in said lobe extending at an angle to and intersecting said first slot a sealing member disposed in said first slot. said sealing member having an edge surface which slidably contacts said curved surface and a third slot in one ancing relation to said first member. 

1. A rotary engine comprising: a housing having an internal chamber defined by a curved surface; a rotor unit mounted for rotation in said chamber and having a plurality of lobes which move with said rotor in follower relation with said curved surface; and a sealing means associated with each lobe for providing a sealing contact with said curved surface, said sealing means comprising a first slot in a lobe of said motor extending radially inward from the apex of said lobe, a second slot in said lobe extending at an angle to and intersecting said first slot, a sealing member disposed in said first slot, said sealing member having an edge surface which slidably contacts said curved surface and a third slot in one side thereof, spring means in said first slot for biasing said first member against said curved surface, a second member disposed in said second slot, said second member having a lip at one end which loosely extends into said third slot and pivotally couples said second member to said first member, said second slot and said second member having cooperating means for providing a pivot for said second member intermediate the ends of said second member, and a counterweight affixed to the opposite end of said second member in counterbalancing relation to said first member. 